﻿//扩展方法示例
namespace Chapter2.exer2_4_1
{
    public class Car
    {
        private double _speed;

        public double Speed
        {
            get { return _speed; }
            set { _speed = value; }
        }

        public double SpeedDown(double down)
        {
            Speed = Speed - down;
            return Speed;
        }
    }
}
